Single speaker systems involving the use of single coil driven speaker are usually involved relatively primitive drive circuits connected between the signal source and the loud speaker. Generally speaking such single speakers systems are built down to a price, and a degree of clarity and performance may be sacrificed. Such speaker systems may involve simple hand held tape recorders, telephone systems, two-way hand held radio communication systems, hand held loud speakers such as are used in crowd control, portable radio, aircraft communication, intercom systems, auto radio, and military mobile radio systems, police radio, and household and apartment communication systems, and in public address systems.
In such single speaker coil driven systems, all of the sound signal frequencies from the amplifier are passed directly through the one coil of the single speaker. This is to be distinguished from the type of situation in more complex audio systems where there are two or three speakers for high, medium and low frequencies. In these systems, complex crossover circuits are used to separate the high, medium and low frequency signals, and direct them to their respective speakers, so that the high, medium, and low range sounds are reproduced separately in the separate speakers.
In a typical single speaker system all of the sounds high, medium and low, are reproduced in the single speaker.
As is well known, the resulting sound as heard by a listener is very far from satisfactory, and is frequently subject to distortion.
It is believed that a significant factor leading to such distortion is the distortion of the signals as they pass through the speaker coil, due to back EMF noise signals induced in the speaker coil as the signals pass through it. In some driver systems for single speakers, there may be one or more coils connected to the speaker coil itself. As the audio signal currents pass through these coils, they will inevitably create further "back EMF" noise.
In U.S. Pat. No. 5,373,563, Inventor, Vladimir W. Kukurudza, Title: SELF DAMPING SPEAKER MATCHING DEVICE, dated Dec. 13, 1994, there is disclosed a crossover system for dividing an audio signal into high, medium, and low frequencies, and directing them to the appropriate speakers, and at the same time, reducing the distortion caused in those speakers by the passage of the audio signal currents through them.
That system has proved to be highly effective with multiple speaker systems having either high or low, or high, medium, and low speakers. However, the system is not suitable for use with single speakers, where crossover circuits are not used.
As mentioned above, the present invention is directed to the method of operating single speaker systems, and the problems of reducing the distortion in such single speaker systems, and is to be distinguished from the problems encountered in multiple speaker systems.